EP1878894B1 - Method of treating oil waste from a gas turbine engine - Google Patents

Description

The present invention relates to the field of aeronautical gas turbine engines and is more particularly to a method of treating bearings lubricating oil discharges.

A gas turbine engine is basically composed of an air compression assembly that feeds a combustion chamber into which air is mixed with a fuel to produce hot gases whose energy is recovered in a turbine assembly. causing the compression means. The shafts connecting the different rotor bodies are supported in the stator parts by bearings mounted in a pressurized enclosure. The enclosures contain the oil that is injected at the bearings to ensure lubrication and include sealing members, maze-type most often, through which air containment. This air is charged with oil particles and in order to keep the oil consumption as low as possible, it is known to use de-oiling equipment which separates the oil from the air that has circulated in the air chambers. bearings. In current engines, this equipment is integrated either inside the engine near the bearings themselves, or at the drive gearbox accessories, also called AGB. The de-oilers do not have a 100% efficiency. The air discharged after passing through the de-oilers still contains oil residues in the form of droplets that are released into the atmosphere. They are therefore the source of pollution and harm the environment.

The applicant has set a goal of reducing the pollutant effect of oil discharges into the atmosphere.

According to the invention, the applicant has developed a method for treating an air flow, charged with oil particles, flowing in a tube in communication with a bearing housing of a gas turbine engine. characterized in that said flow of air is passed through a coking box associated with a heating means, wherein the air is heated to a temperature sufficient to coke the oil particles contained therein . Preferably, the solid residues produced by the coking are collected in the coking box.

Thus the coking transformation of the oil into gaseous and solid residues makes it possible to reduce the harmfulness of gases released into the atmosphere.

On the one hand, coking makes it possible to reduce the volume of oil discharges, on the other hand the residues are less harmful in themselves.

We know the document GB 2,374,026 wherein the flow is passed through a box in which the air is heated to a temperature sufficient to vaporize the oil particles contained in the airflow. However, the oil particles are heated in order to make the emissions in the atmosphere invisible and not reduce their harmfulness. There is no chemical transformation of coking.

According to one embodiment of the method, the box is fixed on said tube so that air passes from the tube into the box. More particularly in a gas turbine engine having an ejection cone downstream of the turbine, the box is disposed in said cone so that it is heated by the gases in the ejection cone.

According to a preferred embodiment, the air is heated to a temperature sufficient to pyrolyze the oil particles, in particular by sampling hot gases immediately downstream of the turbine.

A coking box for treating an air flow containing oil particles flowing in a tube communicating with a bearing housing of a gas turbine engine comprises a cylindrical housing with an opening on one side for receiving airflow from the tube and baffle means. Preferably the box comprises a means for collecting the coked oil and more particularly the housing comprises an end fixing means of the central ventilation tube of the engine and an internal grid through which the oil particles are projected on the inner wall of the housing and forming means for collecting the coked oil.

The invention also relates to a gas turbine engine comprising a central ventilation tube and a gas ejection cone, said tube opening into the ejection channel, characterized in that the coking box is mounted on the central tube so as to be heated by the engine gases of the ejection channel.

Preferably, said coking box is heated by gases taken downstream of the turbine at a temperature sufficient to pyrolyze the oil particles. For example the coking box is arranged on the central ventilation tube near a gas sampling outlet immediately downstream of the turbine where the temperature is of the order of 500 ° C. This solution is interesting insofar as it leads to the elimination of any solid residue. In this case it is therefore no longer necessary to intervene repeatedly on the coking box.

According to another embodiment for a gas turbine engine comprising an accessory drive gearbox AGB, said box is mounted on said AGB.

• La figure 1 représente un moteur à turbine à gaz auquel s'applique l'invention,
• la figure 2 montre la partie arrière d'un moteur avec un tube central de ventilation équipé d'une boîte de cokéfaction de l'invention,
• la figure 3 montre plus en détail une boîte de cokéfaction conforme à l'invention,
• la figure 4 montre un moyen de chauffage de la boîte de cokéfaction selon l'invention.

An embodiment of the invention will now be described in more detail with reference to the drawings in which

• The figure 1 represents a gas turbine engine to which the invention applies,
• the figure 2 shows the rear part of an engine with a central ventilation tube equipped with a coking box of the invention,
• the figure 3 shows in more detail a coking box according to the invention,
• the figure 4 shows a means for heating the coking box according to the invention.

The gas turbine engine of the figure 1 is a turbofan engine turbojet. Such an engine comprises, in this example, a high pressure body with an HP compressor 2 driven by an HP turbine 4 both mounted on the same shaft 6. A shaft 5 concentric with the shaft 6 connects an upstream fan 3, associated to a low pressure compressor 3'BP, to a LP low pressure turbine 7 downstream of the HP turbine 4. The compressed air by the compressors 3 'then 2 goes into an annular combustion chamber 8 where it is mixed with the fuel for produce flue gases. These are guided to the turbine HP4 then BP7 and finally discharged by the downstream nozzle comprising an ejection cone. The propulsion force is provided for the most part for this type of engine by the air flow bypassing the combustion chamber and discharged either directly into the atmosphere by an annular nozzle or mixed with the gas from the turbine and constituting the primary flow. The shafts are supported by inter-shaft bearings for the concentric rotating parts and by bearings mounted on the fixed, statoric structures for the shaft 5.

The bearings, because of the temperatures are lubricated and permanently cooled by oil that is confined in a chamber called bearing enclosure. Pressurized air is introduced at the seals to form a barrier and prevent oil from passing to the hot engine parts and causing a fire. After passing through an oil recovery de-oiler, the containment air is usually vented to the atmosphere through the central ventilation tube 9. This is the case when the de-oiler is placed near the bearing housings. In the following description, the invention is applied to this case but it also applies to the case where the de-oilers are arranged on the AGB housing.

The air ducted by the tube 9 is discharged downstream by a central duct disposed in the frustoconical piece 10 or substantially frustoconical, defining the inner surface of the gas stream from the turbine stages. In the solutions of the prior art, the residual oil, even in small quantities, is sent into the atmosphere through the ejection cone.

According to the invention, any residual oil is removed from the air before it is released into the atmosphere by trapping it and oxidizing it into gaseous species and into coke of lower toxicity than the oil.

One way to achieve this is illustrated on the figure 2 which shows in more detail the rear part of an engine such as that of the figure 1 . There is the rear bearing 12 supporting the pin 14 of the LP turbine. The bearings 12a of the bearing 12 are mounted in a cage disposed between the fixed bearing support 13 and the trunnion 14. The assembly is contained in an enclosure 15. Labyrinth seals 15a, 15b are formed between the fixed structure of the enclosure and the LP rotor disc. Labyrinth seals 15c and 15d are also provided between the fixed structure and the central ventilation tube which is integral with the LP shaft. The air from the chamber is removed by the de-oiler 16 and is evacuated centrally by the tube 9. The elements that have just been described are not part of the invention and are known per se.

The air from the tube 9 is driven downstream inside the ejection cone and is mixed with the engine gases.

In accordance with the invention, there is provided a box, hereinafter referred to as a coking box 20, on the downstream end of the central ventilation tube 9. This box is shown in detail on FIG. figure 3 .

It comprises a cylindrical housing 21 of diameter slightly greater than that of the tube 9. The housing is fixed at the end of the tube by any suitable removable means. It is mounted open on the tube. Inside the housing a cylindrical grid 22 provides an annular space 22a with the housing. Over the length of the housing 21, transverse plates 24 regularly spaced are fixed in the volume defined by the grid 22, alternately in the form of baffles. The housing is closed downstream by a grid with axial holes and defining a flame arrester 26. The housing 21 is thus mounted downstream on the tube 9 so as to collect the air flowing therethrough. This air is forced inside the housing by the plates 24 in a path alternately radially outward and radially inward. It follows that the oil particles that it contains are centrifuged through the grid 22. They are collected in the annular space 22a. By its arrangement at the end of the tube 9, the housing is heated by the ambient gases inside the ejection cone which thus maintain, in operation of the engine, the wall of the housing 21 at a temperature of about 300 ° C. At this temperature, the oil in the space 22a undergoes a thermal oxidation transformation. It is partly converted into CV coked coke oil and partly into CS coke, a solid residue.

One way to remove the solid residue is to disassemble the box and change it. It is an operation that is performed easily on the ground during engine maintenance operations under the wing of the aircraft. According to a more economically advantageous embodiment, the box can be made in the form of a removable and replaceable cartridge. However, it must also be taken into account that under certain operating conditions of the turbojet engine or in the event of failure (excess oil consumption) the quantity of coke formed may not be negligible. This implies either relatively frequent or unforeseen interventions, penalizing for profitability, or an increase in the volume of the box resulting in a congestion and a mass equally penalizing.

An advantageous way of removing the solid residue more rapidly is to pyrolyze it as it is formed by raising it to a high temperature. Indeed above 500 ° C the coke is burned without leaving any residue. Thus according to a particular embodiment, the device comprises means for heating the box up to 500 ° C. We have shown on the figure 4 , a mounting of the box inside the exhaust cone as in the previous case but by adding a tube 18 to bring a determined amount of gas from the vein of the primary flow on the walls of the box.

Claims (11)

1. A method for treating an airflow, laden with oil particles, flowing in a tube (9) communicating with a rolling bearing enclosure of a gas turbine engine, wherein said airflow is made to travel into a coking box (20) associated with a heating means, in which the air is heated to a sufficient temperature to coke the oil particles contained in the airflow.
2. The method as claimed in the preceding claim, wherein the solid residues produced by the coking are collected in the coking box (20).
3. The method as claimed in one of the preceding claims, wherein said box (20) is attached to said tube (9) so that the airflow travels from the tube into the box.
4. The method as claimed in the preceding claim for treating said airflow in a gas turbine engine comprising an exhaust cone (10) downstream of the turbine, wherein the box is placed in said exhaust cone (10) so that it is heated by the gases in the exhaust cone.
5. The method as claimed in claim 1, wherein the air is heated to a sufficient temperature to pyrolize the oil particles.
6. The method as claimed in claim 5, wherein the air is heated by taking hot gases immediately downstream of the turbine.
7. A gas turbine engine comprising a central ventilation tube (9) communicating with a rolling bearing enclosure of the engine and a gas exhaust cone (10), said tube opening into the exhaust channel, wherein it comprises a coking box for the treatment of the airflow originating from the rolling bearing enclosure that contains the oil particles, the coking box (20) comprising a cylindrical casing (21) with an opening on one side to receive the airflow from the tube (9) and a means (24) forming chicanes, and being mounted on the central tube (9) so as to be heated by the engine gases from the exhaust cone (10).
8. The engine as claimed in the preceding claim whose coking box comprises a means (22) for collecting the coked oil.
9. The engine as claimed in the preceding claim, whose casing (21) comprises an attachment means at the end of said tube (9) and an internal grid through which the oil particles are sprayed onto the internal wall of the casing and forming a means for collecting the coked oil.
10. The engine as claimed in claim 7, 8 or 9, wherein said coking box (20) is heated by gases taken downstream of the turbine at a sufficient temperature to pyrolize the oil particles.
11. The gas turbine engine as claimed in one of claims 7 to 10 comprising an accessory gearbox (AGB) wherein said coking box is mounted on said gearbox.

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